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How to identify it
- Adults are about 1/4 inch long; UC IPM gives 0.2 to 0.33 inch. UC IPM describes them as shiny or grayish black with black or red legs and prominent eyes, and the PNW handbook describes Labops as grayish black with silvery scales.[1][3][4]
- Labops hesperius, the most common species in Colorado, has light margins on the wings and abdomen. Irbisia brachycera is all or mostly black. Labops species look very much alike.[1][2]
- Females tend to lack fully formed wings, which limits their spread, and adults can have short or missing wings. The PNW handbook describes the body as somewhat pear-shaped.[2][4]
- Nymphs look like smaller versions of the adults.[1][2]
Look-alikes
| Look-alike | How to tell them apart |
|---|---|
| Frost injury | Frost and black grass bug feeding can both leave straw-colored leaves. Bug feeding starts as white spots at individual feeding sites on the upper leaf surface and is usually worst at field edges. Sweep the grass with a net to find the bugs, which drop to the soil when disturbed.[2][1][3] |
Where it lives
Colorado State describes them as native to western rangeland and reported in Arizona, Colorado, Idaho, Montana, Nebraska, New Mexico, North Dakota, Oregon, South Dakota, Utah, Washington and Wyoming. UC IPM covers them in California small grains, and the Pacific Northwest handbook lists them as rangeland pests.[1][3][4]
Biology and life cycle
There is one generation a year. Eggs spend the winter inside grass stems and hatch in spring as the grass starts to grow; hatch comes earlier in warm springs and later in cold ones.[1][2]
Nymphs go through five stages and reach adulthood in about four to five weeks. Young nymphs shelter in grass litter and soil cracks, and peak feeding comes in late spring and early summer.[1][2]
Females lay their eggs in the center of dried stems, about 20 each over a lifespan of roughly a month. The bugs are most active in the evening.[1]
They prefer grasses, above all crested wheatgrass, and solid stands of crested wheatgrass can support large, destructive populations. Other hosts include wheatgrasses, Great Basin wildrye, brome, orchardgrass, bluegrass, and barley, wheat, rye and oats. When grasses are scarce they can feed on broadleaf plants.[1][4][2]
In Colorado, infestations have spread from plots of less than an acre to thousands of acres in only a few years.[1]
Damage and signs
- They feed with piercing-sucking mouthparts on the upper surface of the leaves. A white spot forms at the feeding site within seconds, and feeding destroys chlorophyll, leaving whitish or yellowish patches and a stippled look.[2][1][3][4]
- Heavily fed leaves turn straw-colored, much like frost damage. Damage is usually worst at the edges of fields, and it is more severe on drought-stressed grass.[1][2][3]
- On rangeland, feeding lowers grass vigor and makes it less palatable to cattle, and heavy infestations can prevent seed formation. Together with drought or grazing, repeated infestations can kill the plants. Crops next to infested rangeland can also be damaged.[1]
Health risk
The cited sources describe them only as pests of grasses and grain crops and mention no risk to people or animals.[1][2][3][4]
Control
Prevention
Check grass in spring as temperatures warm and eggs hatch. Look for discolored, stippled leaves and sweep with an insect net, starting at the edge of a field and working toward the middle. No action thresholds have been set.[2][1][3]
On crested wheatgrass pasture, grazing that leaves the vegetation uniformly short, rather than patchy grazing or resting the pasture, can significantly reduce the bugs' impact. It may also destroy new plantings of crested wheatgrass and reduce habitat for natural enemies such as assassin bugs.[1]
Traps and physical control
Mowing can reduce the number of eggs in the grass stems, and on hay ground, mowing and removing the hay may do the same. In lawns, watering adequately helps the grass recover from feeding.[2][1]
Pesticides
Spraying every year is typically unnecessary, because populations take several years to build to damaging numbers and cultural controls usually suffice. Insecticides kill adults but not the eggs in grass stems, so if enough eggs are present, fields or lawns can be reinfested the next year. On rangeland, Colorado State does not typically recommend insecticides because of cost and environmental concerns, though one well-timed application may keep numbers low for many years. In lawns hit before, Colorado State says certain insecticides applied at spring emergence can be effective, and the PNW handbook lists bifenthrin, carbaryl, lambda-cyhalothrin and malathion for rangeland. UC IPM's small-grain guidelines say no pesticides are registered for black grass bug on small grains.[2][1][4][3]
Common questions
- Why does my lawn look frost-damaged in late spring?
- Black grass bugs are one possible cause in the West. Their feeding leaves white spots on the upper leaf surface, and the leaves can turn straw-colored, resembling frost damage. Sweep the grass with a net to look for the small black bugs.[2][1]
- Do I need to spray every year for black grass bugs?
- Usually not. Populations take several years to reach damaging numbers, and mowing and adequate moisture are often enough. Sprays kill adults only, not the eggs in grass stems.[2]
- Why are black grass bugs worse in crested wheatgrass?
- They strongly prefer crested wheatgrass, and solid stands of it can support large, destructive populations. Grazing such pastures evenly short can significantly reduce their impact.[1]
Sources
- Colorado State University Agricultural Biology, “Black grass bugs.” agsci.colostate.edu/agbio/ipm-pests/black-grass-bugs/ (accessed 2026-11-08)
- Colorado State University Agricultural Biology, “Black grass bugs in turfgrass.” agsci.colostate.edu/agbio/ipm-pests/black-grass-bugs-2/ (accessed 2026-11-08)
- University of California Statewide IPM Program, “Black Grass Bug (Pest Management Guidelines: Small Grains).” ipm.ucanr.edu/agriculture/small-grains/black-grass-bug (accessed 2026-11-08)
- Pacific Northwest Pest Management Handbooks, “Rangeland-Black grass bug (Pacific Northwest Insect Management Handbook).” pnwhandbooks.org/insect/hay-pasture/rangeland/rangeland-black-grass-bug (accessed 2026-11-08)
- iNaturalist, “Labops hesperius taxon page (order and family).” www.inaturalist.org/taxa/68167 (accessed 2026-11-08)